1. Field of the Invention
Exemplary embodiments of the present invention relate to a wireless communication system; and, more particularly, to an apparatus and method for normally transmitting and receiving data by compensating a Carrier Frequency Offset (CFO) for a wireless channel in a wireless communication system.
2. Description of Related Art
Many studies have been actively made for providing services with QoS (Quality of Service) to users in a next generation communication system. Particularly, many studies for a wireless local area network (WLAN) have been made through Institute of Electrical and Electronics Engineers (IEEE) 802.11 specification. Regarding a WLAN system, many studies for transmitting data through a wireless channel have been in progress. Lately, methods for transmitting and receiving data effectively using a limited wireless channel in an IEEE 802.11 system have been introduced.
Recently, an Orthogonal Frequency Division Multiplexing (OFDM) communication system has been applied to a wireless communication system. Such an OFDM communication system transmits and receives a mass amount of data through a wide bandwidth. In the OFDM communication system, each subcarrier of a wireless channel has an orthogonal property in order to transmit and receive a mass amount of data. In order to improve a data transmit rate of a limited wireless channel, the OFDM communication system determines a channel state of a wireless channel and control transmitting and receiving data based on the determined channel state of the wireless channel.
As an example of controlling transmitting/receiving data based on a wireless channel state, an OFDM communication system estimates a Carrier Frequency Offset (CFO) by a unit of a packet and restores a transmitted data packet by compensating the estimated CFO. However, it is difficult to accurately estimate a CFO when a wireless channel state is very poor, for example when a signal to noise ratio (SNR) of a wireless channel is smaller than a predetermined threshold value or when fading is seriously generated in a wireless channel environment. When the transmitted data packet is restored by compensating an inaccurately compensated CFO, a data packet restoration error rate increases. When signal field information is incorrectly restored, a restoration error would be continuously generated.
As described above, when a CFO is estimated from a data packet transmitted through a wireless channel having a poor state, for example, a wireless channel having serious fading, it is difficult to accurately estimate CFO. When the transmitted data packet is restored based on an inaccurate CFO, a data packet error is generated. It causes a data packet error rate increased. As a result, a data transmit rate becomes decreased. Particularly, if a terminal in an OFDM communication system is a mobile terminal, fading is further seriously generated and a poor wireless channel state abruptly varies. Accordingly, the inaccurate estimation of CFO and the data packet error are further frequently generated. As a result, a data transmit rate becomes significantly deteriorated and an overall system performance also becomes rapidly dropped.
Therefore, there have been demands for developing a data transmitting/receiving method for minimizing errors to be generated while restoring a data packet and improving a data transmit rate by accurately estimating a CFO of a data packet transmitted through a wireless channel in a wireless communication system such as an OFDM communication system.